Tagging vs. semantic Web

are labels with words or a combination of words that are attributed/attached to pieces of content – most often retrospectively by users;

describe content implicitly and hence are ambiguous (like any term in human language)

;

tagging is a light version of the semantic Web.

The semantic web

is like a logical layer that sits on top of the Web (of documents);

the semantic Web is a Web of structured data and a data-field is the smallest semantic unit in the Web;

using (standard) identifiers and expressions of relationship between data fields, description of content is made explicit and non-ambiguous;

the semantic Web is based on interoperable metadata standards such as identifiers and expressions of relationships.

The way from the Web of Documents to the Semantic Web requires a shift in thinking: from “thinking repository scale to thinking Web scale” (Silver Oliver)

Side note: Interestingly, according to semiotic thinking, human language terms (as utilised in tags) become meaningful in differentiation to competing semantic units, i.e. by implicit logical exclusion – ‘is not this, is not that’ – whereas in the semantic Web meaning is defered by explicit attribution of identifier and a limited number of expressions of relationships.